The following discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.
The integration of MEMS and infrared detector technology, where the MEMS structure is used as a resonant cavity to improve quantum efficiency, has the following applications:                High performance infrared detectors        High performance infrared detectors operating with reduced cooling requirements—high operating temperature (HOT) detectors        Wavelength agile versions of the above applications.        
International Patent Application PCT/AU03/00048 filed by the applicant describes, inter alia, the formation of n-p junctions, and particularly n-on-p junctions which has particular, but not exclusive, utility in the construction of infrared (IR) photodiodes and detectors that function as two-dimensional staring arrays fabricated using mercury cadmium telluride (MCT). Accordingly, the entire disclosure contained in International Patent Application PCT/AU03/00048 is incorporated herein by reference to constitute part of the disclosure of this specification.
International Patent Application PCT/AU03/00280 also filed by the applicant describes the application of MEMS structures with infrared wavelength detector technology to arrive at a tunable resonant cavity design having widespread utility not only in the field of infrared wavelength detector technology, but in other areas of electromagnetic filtering. Accordingly, the entire disclosure contained in International Patent Application PCT/AU03/00280 is also incorporated herein by reference to constitute part of the disclosure of this specification.
The specifications of the aforementioned international patent applications describe, inter alia, technology for the development of high performance mid-wavelength infrared (MWIR—3-5 μm) HgCdTe detectors, as well as long-wavelength infrared (LWIR, 8-12 μm) detectors using a reactive ion etching process to form n-on-p junctions. MWIR photodiodes developed according to the described processes give state of the art performance.
The specification for International Patent Application PCT/AU03/00280 also describes the development of low-temperature fabricated MEMS structures applicable to a wide range of semiconductor material systems that cannot withstand the high temperature processing usually required for MEMS devices. The invention has resulted in the development of new technologies for the fabrication of micro-machined optical micro-cavities with electrostatically actuated membrane mirrors as described in the specification. A cross-sectional view of a micro-machined Fabry-Perot cavity interferometer integrated with a photodiode formed according to the invention that is the subject of International Patent Application PCT/AU03/00280 to create a detector device with the detector externally disposed of the cavity is shown in FIG. 1. In the devices that can be fabricated in accordance with this invention, with specially designed supports, membrane movement of ˜75 μm can be achieved using 50V bias without cracking of the membranes. Experiments on micro-cavities have also shown that changes in cavity length of more than 300 nm using voltages less than 5V can be achieved while maintaining mirror parallelism of better than ±5 nm over 100×100 μm2.
The noise in the signal from current state-of-the-art IR photon detectors is related to generation-recombination mechanisms in the material forming such detectors, and is directly proportional to the detector volume. The optical area of the detector is generally set by the optical system requirements leaving device thickness as the only parameter available for optimisation of noise performance. Since the signal strength depends on the amount of absorption of photons, in a standard detector there exists an optimum thickness which results in a maximum signal to noise ratio.